1. Field of the Invention
The present invention relates to a manufacturing method of ceramic slurry, more particularly, a manufacturing method of ceramic slurry being used for producing a green sheet which can have a smooth surface, exhibits a satisfactory sheet strength, and is excellent in workability such as releasing, a green sheet produced by the use of a slurry produced by the method, and a multilayer ceramic device produced by the use of the green sheet.
2. Description of the Related Art
Developments of ceramic green sheet are performed to obtain a high-capacitance multilayer ceramic chip capacitor as an example of multilayer ceramic device. The multilayer ceramic chip capacitor has a structure of alternately laminating electrode layers, which one end is exposed to the edge of the chip, and dielectric layers, and both sides of the laminating direction are covered with the dielectric layers like a lid.
While more dielectric layers in 1 chip can provide a higher capacity, the chip size is fixed. Therefore, in order to make capacitance of the chip large or maintain the capacitance while miniaturizing the chip, the dielectric layer is required to be thin. The dielectric layer is obtained by covering dielectric particles having a diameter of sub micron order with resin, i.e. binder, to form a sheet, laminating these sheets, and firing. Therefore, in order to laminate said dielectric layers, it becomes important to produce a thin green sheet.
However, when the sheet becomes thin, unevenness on the sheet surface cannot be ignored. That is, when the sheet is thin, a surface state change, which was not needed to take into consideration when the sheet was thick, turns into change of the sheet thickness itself. It is expected that concaves of the unevenness on the surface becomes weak to voltage impression after firing, and causes short circuit. Therefore, it is indispensable requirements for manufacturing multilayer chip capacitor to provide a sheet having a smooth surface, i.e. small change of a surface roughness, and a uniform thickness.
As factors, which influence the surface unevenness of a sheet, a particle size of pigments, a paste composition, a dispersing condition when manufacturing the paste, a spreading condition when forming a sheet, and a smoothing treatment to the sheet itself, etc. are mentioned. The present invention relates to an improvement approach of the distributed condition when manufacturing the paste. Pigments not causing aggregation within the paste and disperse as a single particle form raises surface characteristic and density of the sheet formed with said pigments. With the present invention, pigments can be dispersed, and sheet having superior surface characteristic can be manufactured.
In addition, as shown in the following patent reference 1, a method to improve dispersiveness by performing a high-pressure treatment particularly to the binder while manufacturing the paste is proposed. However, with the technique shown in this patent reference 1, since a high-pressure dispersion treatment is applied to the paste including binder. i.e. resin, as shown in FIG. 2(B), shearing stress is given to not only pigments but also resin. For this reason, the resin will be destroyed by the shearing stress, and deterioration in sheet strength may be caused.
Patent Reference 1: U.S. Pat. No. 3,387,455